The present invention relates to an evaluation method for a particle counter in which a detector signal is produced by means of a detector. The detector reacts to the presence of particles in a measuring zone in which a liquid flow is being conveyed. The detector signal is treated by a signal processing device and, taking into account at least one calibration factor, is converted into a display value indicating the particle density of the liquid flow. The present invention also relates to a device for carrying out the evaluation method.
European Patent 0 427 908 discloses a particle counter working by the opacity method and including a light enclosure. The light enclosure receiver produces detector signals showing the presence of opaque particles in the measuring zone. An evaluation method of this type is used in the evaluation of these detector signals, carried out by the method disclosed in DE 41 10 231 A1. The degree of contamination of the liquid flow flowing through the measuring zone is to be monitored, preferably with hydraulic petroleum. The densities of charges of solid materials, such as metallic and nonmetallic impurities or contaminants, in the liquid are established. Even the presence of air bubbles or water droplets in the light enclosures likewise lead to the appearances of opacities which appear on the detector signal.
In the conventional evaluation method, particles present in a certain volume to be measured are counted in channels of different magnitudes, associated with particles which are in classes of different magnitudes and in turn are counted as pulses of the detector signal. The volume to be measured in turn is determined by volume flow measurement. The particle count is then corrected by multiplication with the relevant channel magnitudes of corresponding individual calibration factors. These corrected particle numbers are then translated into classes of contamination in order to correspond to the NAS 1638- or ISO 4406-Tables.
DE 1 294 051 B discloses a method and device for the measurement of the volume or weight of a volume of essentially nonuniform bodies being conveyed through a channel of predetermined diameter. In this case, the detector signal is converted by means of a trigger stage into pulses of constant amplitude. These pulses are fed to an integrator, in which occurs a time integration of the discrete individual pulses. Following each pulse, the output signal of the integrator is returned to start. The method supplies an output signal which represents a mean value of the volume or weight of the bodies conveyed in a time lapse to be studied.
GB 2 082 764 A discloses a device for measuring particles in liquids in which the appearance of particles is established as a phenomenon, and the phenomena are summarized by means of a counter. When a predetermined number of phenomena has been exceeded, a switch is activated, which can set off an alarm or react otherwise. For determination of the particle density, additional and independent measurements of the volume flow must be carried out.
Objects of the present invention are to provide a method of evaluation which, as opposed to the conventional method, is characterized in that the density of the particle charge of the relevant liquid flow can be evaluated at lower cost and with greater precision.
With an evaluation method of this type, these objects are attained according to the present invention by the treatment of the detector signal being carried out in such a manner that the individual residence times of the particles in the measuring zone are determined within a predetermined lapse of time. By summation of the residence times, a summation signal is formed. This summation signal is used, taking into account at least one calibration factor, for the representation of the display value.
Since the display value is no longer determined on the basis of the counted number of particles present in a certain liquid volume, but rather on the basis of a summation of the individual residence times of the particles within the zone of measurement carried out within a certain predetermined lapse of time, the measurement of the volume flow, which is required in the conventional method, as well as other measures which have been required in cooperation with the conventional method, can be deleted. Thus, the method according to the present invention is characterized not only by simplified capacity of execution with decreased outlay of apparatus, but also by a comparably higher precision in the results. Since no knowledge concerning the present volume flow is required, the evaluation is dependent neither on any measurement or limitation of the volume flow being considered nor of its condition otherwise. Regarding a higher level of precision, the circumstance is also to be considered that no error of the volume flow measurement need be taken into consideration for the calculations.
One method for ascertaining the distribution of the particle dimensions of the particles dispersed in liquids is disclosed in DE 32 09 510 C2 and U.S. Pat. No. 4,491,926, by determining the residence times of particles in the measuring zone. Differing from that disclosure, the method according to the present invention carries out the treatment of the detector signal in such a manner that residence times of the particles in the measuring zone are determined on the basis of the number of counted pulses.
As in the conventional evaluation method, in the present invention the evaluation can be based on the different classes according to particle size, as found in the so-called magnitude-channels. A suitable calibration factor is used for each relevant channel magnitude, for the determination of the display value. Thus, the particle number per liquid volume can be deduced from the summation signal, for example the count per 100 ml, so that in turn the correlation to classes of contaminants relating to this particle number can be undertaken corresponding to the NAS 1638- or ISO 4406-Tables relating thereto.
For evaluation of the pulse height in the detector signal for correlation to the channel magnitudes, the detector signal can be converted by means of a comparator circuit into a comparator output signal representing the residence times while taking into account a predetermined threshold value. The output signal is used for the summation of the residence times and can be analog or digital. With the analog determination, the comparator output signal is integrated within the predetermined lapse of time to a voltage value representing a summation signal. With the digital determination, according to one preferred embodiment, it is carried out so that the summation of the residence times is demonstrated in such a manner that oscillator pulses are counted, which have been released within the predetermined lapse of time according to the measure of the comparator output signal.
According to one other aspect of the present invention, a device for execution of the disclosed evaluation method is provided. The device of the present invention includes a signal processing device with a comparator circuit for generation of a comparator output signal representing the residence times of the particles in the measuring zone, while taking into consideration a predetermined threshold value. A pulse generator produces a pulse signal defining the predetermined lapse of time, as well as with a summation device.